Method of hot-briquetting mixtures of coal and coke

ABSTRACT

Coke is mixed with bituminous coal and the mixture is converted into briquettes. To obtain high-quality and high-strength briquettes, the temperature of the coke is adjusted, prior to mixing, to such a level that when the mixing takes place, the coke/coal mixture will have a precisely predetermined temperature within the scope of 400°-500° C. The exact temperature within this range is selected in dependence upon the characteristics of the coke and the coal.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the briquetting of mixtures of coal andcoke.

More particularly, the invention relates to the hot-briquetting of suchcoal/coke mixtures.

2. The Prior Art

It is known from the prior art to convert coal into coke--e.g., in afluidized-bed reactor or in a stream of hot gas--to obtain hotbriquetting coke which is then mixed with coking (i.e., bituminous) coalwhereupon the resulting mixture is briquetted at a temperature of about400°-500° C.

The amount of coking coal which is added to form the mixture variesbetween 20 and 40% by weight of the mixture, depending upon thecharacteristics of the coal. The weight percentage must be the higher,the lower the bitumen content of the coal in order to obtain briquettsof adequate strength (i.e., resistance to crumbling, breaking andabrasion).

In the prior art the coal will have a temperature within the range of10°-100° C. prior to mixing with the coke which itself will have atemperature of between about 700°-800° C. The coal temperature dependsupon the source from which the coal is fed; a 100° C. temperature willobtain if the coal is added to the coke immediately after undergoing adrying operation. Because of the temperatures of the coal and cokerelative to one another, the temperature of 400°-500° C. desired for thecoal/coke mixture can be readily attained as a result of the mixing.

However, difficulties have been experienced in obtaining briquettes ofuniform quality, especially uniform strength, with the prior-artapproach. Upon long and detailed investigation of the problem it wasfound that contrary to previous belief the quality and strength of thebriquettes are dependent not merely upon the weight percentage of coalin the briquetting mixture (making allowance for the characteristics ofthe particular coal). The quality and strength of the briquettes are,surprisingly, also influenced--and at least equally so--by anotherfactor, namely the briquetting temperature which must be individuallyaccommodated (upon empirical determination) to the characteristics ofthe coal and the coke in a particular mixture. It has been found to beof central importance that the temperature of the mixture beingbriquetted not only be prevented as much as possible from fluctuating,but that it be adjusted to within substantially ±5° C. to an individualbriquetting temperature. Contrary to previously held beliefs it is notpossible to obtain briquettes of consistently maximum quality andstrength by adjusting the temperature to within e.g., ±20° C. in the400°-500° C. range.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to overcome thedisadvantages of the prior art.

More particularly, it is an object of the invention to provide animproved briquetting method of the type under discussion, which avoidsthe aforementioned disadvantages and permits the manufacture ofbriquettes of consistently high quality and strength.

In keeping with these objects, and with others which will becomeapparent hereafter, one feature of the invention resides, brieflystated, in a method of making briquettes in which coke and coking coalare admixed to form a briquetting mixture having a temperature in therange between about 400°-500° C., the improvement wherein the coketemperature is adjusted, prior to mixing of the coke with the cokingcoal, to a temperature level which will, upon mixing of the coke withthe coking coal, result in the mixture having a selected briquettingtemperature in the range between about 400° and 500° C.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

The single FIGURE is a diagrammatic illustration of an installation forcarrying out the novel method.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The FIGURE illustrates an installation which is suitable for carryingout the inventive method. The individual elements of the installationare known per se and, therefore, require no detailed description.

Coking coal is admitted into a reactor 1, as indicated by the arrow,wherein it is heated to be thereupon transferred via conduits 2, 4 intoa thermal conditioning vessel 5. As shown, a cyclone 3 may be interposedbetween the reactor 1 and the vessel 5, for withdrawal of gases anddischarge of other substances at 15.

In the vessel 5 the heated coking coal slides from the top to the bottomof the vessel in form of a coal layer and becomes cooled due to contactwith appropriate heat-exchange surfaces (e.g., baffles through whichcooling liquid, such as water, circulates. The cooled coking coal isthen transferred via conduit 6 into a mixer 7 (e.g., a screw-type mixer)which also receives coking (bituminous) coal via a conduit 8 from areservoir 9. The coking coal and the baking coal undergo intensivemixing in the mixer 7 and the mixture then forwarded to an agitatingvessel 11 (e.g., equipped with stirrers) from where it passes via outlet12 into the not-illustrated briquetting press. A conductor 13 connectsthe vessel 5 with a temperature sensor 14 of the vessel 11 so that thedegree of cooling to which the coking coal is subjected in the vessel 5can be automatically regulated in dependence upon the mixturetemperature detected by the sensor 14 which may extend into contact withthe mixture in vessel 11. This automatic regulation via thejust-described simple--and optional--feed-back circuit may be especiallydesirable if for manufacturing reasons, or to reduce the strain on thecooling equipment, it is desired to change from hot dry coking coal(reservoir 9) to a partially moist coking coal or to a non-dried cokingcoal.

The invention will now be further described on hand of severalillustrative examples.

EXAMPLE 1

A semibituminous coal having 16% by weight of volatile contents and aparticle size smaller than 10 mm was admitted into the reactor 1 andheated to 750° C. It was thereupon transferred to the vessel 5 whereinit was cooled to 640° C. with a concomitant development of 0.7 t/h ofsaturated steam (from heating of the cooling fluid which was water) at apressure of 10 bar. Upon being cooled to 640° C. the coke wastransferred via conduit 6 to mixer 7 into which baking coal was at thesame time admitted from reservoir 9 via conduit 8. The mixture of cokeand coal was transferred from mixer 7 via conduit 10 to the agitatingvessel 11, and from there via conduit 12 to a briquetting press.

The reactor 1 received 10 t/h of the semibituminous coal; of thisamount, 2 t were distilled off as gas, tar and oil--H₂ O. The residual 8t/h of coal, now converted into coke, were mixed in mixer 7 with 2 t/hof baking coal having a particle size smaller than 1 mm and a volatilecontent of 25-28% by weight, which was admitted from reservoir 9 at atemperature of 110° C. Therefore, the mixing ratio of coke to bakingcoal was 75:25; the mixing and subsequently the briquetting temperaturewas about 460° C.

The (not illustrated) briquetting press converted the mixture into 9.5t/h of hot briquettes which were cooled to ambient temperature in ashaft furnace. Tests conducted on the thus obtained briquettes showedthem to have a mechanical (breaking) strength of 3000 N and an abrasionloss (M₁₀) of 5% by weight, measured according to German Industrial Norm(DIN) 51717.

EXAMPLE 2

Flame coal having a particle size smaller than 8 mm and containing 42%by weight of volatiles, was admitted in quantities of 15 t/h intoreactor 1, and heated to 600° C. in order to obtain a maximum yield oftar. This produced 2.8 t/h of tar and oil, in addition to gas, water andcoke. The coke, amounting to 9.5 t/h, was heated to 830° C. by admittingit into the top of the reactor vessel 5 for gravity-descent to thebottom of the same, while at the same time a quantity of 1000 m³ /h ofair was passed through the reactor vessel 5 in counterflow to the coal.This resulted in partial oxydation of the coke which raised itstemperature to 830° C.

The thus heated 9.5 t/h of coke were mixed in the mixer 7 with 6.3 t/hof baking coal at 105° C. and having a particle size smaller than 1 mmand a volatile content of between 24-28% by weight. The mixing ratio ofcoke to coal was 60:40%, the mixing and briquetting temperature wasabout 470° C.

The mixture was converted into 14 t/h of hot briquettes having amechanical strength of 3500 N and an abrasion loss of 7% by weight (M₁₀)measured according to DIN 51717.

EXAMPLE 3

Semibituminous coal having a particle size smaller than 10 mm and avolatile content of 16% by weight, was admitted into reactor 1 in aquantity of 10 t/h. It was heated to 780° C., resulting indistilling-off of 2 t/h of gas, tar and oil-H₂ O. The remaining 8 t/h ofcoke were transferred into vessel 5 to rum from the top to the bottom ofthe same by gravity descent. Coking water was sprayed into the vessel 5in an amount of 0.75 m³ /h to cool the coke to 640° C.; a desirableincidental result was the thermal decomposition of ecologicallyundesirable components in the water during conversion of the water intosteam.

The remaining 8 t/h of cooled coke were then transferred to the mixer 7into which baking coal at 110° C. was admitted from reservoir 9. Thebaking coal had a particle size smaller than 1 mm and between 75-25% byweight of volatiles. It was admitted in a quantity of 2 t/h so that themixing ratio of coke to coal was 75:25; the mixing and briquettingtemperature was about 460° C.

The mixture was converted in the briquetting press into 9.5 t/h of hotbriquettes which were cooled to ambient temperature in a shaft furnace.The mechanical strength of the briquettes was found to be 3000 N andtheir abrasion loss (M₁₀), tested according to DIN 51717, was 5% byweight.

It will be appreciated from the foregoing that the thermal conditioningof the coke in the vessel 5 can be carried out in various differentways.

The vessel may be provided with conduits which extend into the coke tocontact it and through which a heat-exchange fluid is circulated. Thisoffers indirect cooling of the coke the efficiency of which may befurther improved by agitating the coke via an inert gas that is blowninto the vessel. If the heat-exchange fluid is water, the heat removedfrom the coke can be recovered since steam will be produced which isavailable for other useful purposes.

The vessel 5 may also be of the type through which the coke passes infree fall. In that event, coking water may be sprayed onto the coke tocool it and deleterious substances dissolved in the water are thermallydecomposed and rendered harmless without posing any ecological problems.

The vessel 5 may, however, also be of the type through which the cokeflows under the influence of gravity to be agitated and directed bybuilt-in baffles. This will be the case when the coke must be heated,rather than cooled. A precisely controlled quantity of air is admittedin counterflow into the vessel so that combustion heat is obtained dueto partial oxydation of the coke.

Of course, a fluidized-bed reactor or a travelling bed (layer) reactorcan also be employed as the vessel 5.

The invention assures in all instances that the briquette quality ismade independent of the temperature fluctuation of the hot coke, as wellas of the baking coal. Thus, the temperature found to be mostadvantageous for producing from a specific ratio of coke and coal,wherein the coke and coal of the given mixture have specificcharacteristics, can be precisely controlled to obtain briquettes ofmaximum quality, including maximum strength.

In addition, the invention has still further advantages.

Coking of coal results in the liberation of a series of by-products. Tarand gas are the most valuable of these. It may be desirable--to obtainhigh-quality tar--to coke in such a manner that the final coke issuingfrom the reactor will have a relatively high temperature. If so, thiscan be readily achieved without thereby disadvantageously influencingthe quality of briquettes made from a mixture of this coke with cokingcoal. For example, should it be necessary to obtain a final coketemperature of between about 700°-900° C. so as to produce--during thecoking--a high-temperature tar having a desired quality, the resultingcoke--which is too hot to yield a satisfactory briquetting mixture--canbe readily cooled to lower temperature which has been found to be themost advantageous in terms of obtaining high-quality briquettes.

Again, to obtain from bituminous coal a maximum yield of liquidby-products (e.g., tar, oil) during coking, it is necessary to effectcoking at temperatures of about 600° C. This will, however, then yield acoke which is too cool for subsequent mixing and hot-briquetting. This,also, can be corrected by resorting to the present invention, in thatthe coke temperature can be raised, instead of lowered, until a level isreached at which a mixture of this coke and the coking coal will producehigh-quality briquettes.

Thus, the invention makes possible a much greater flexibility in thebriquetting process than existed before. It enables the operator toselect and maintain the optimum briquetting temperature withoutdifficulty, even though the temperature of the coke and/or the quality(i.e., characteristics) of the coking coal may fluctuate during thebriquetting operation, e.g., during a given production run.

While the invention has been illustrated and described as embodied in amethod of hot-briquetting, it is not intended to be limited to thedetails shown, since various modifications and structural changes may bemade without departing in any way from the spirit of the presentinvention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this invention.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims:
 1. In a method of making briquettes inwhich coke and coking coal are admixed to form a briquetting mixturehaving a temperature in the range between about 400°-500° C., theimprovement wherein the coke temperature is adjusted, prior to mixing ofthe coke with the coking coal, to a temperature level which will, uponmixing of the coke with the coking coal, result in the mixture having atemperature within ±5% of a predetermined briquetting temperature lyingwithin said range.
 2. A method as defined in claim 1, wherein the cokeis indirectly cooled by contact with heat-exchangers.
 3. A method asdefined in claim 1, wherein the coke is directly cooled.
 4. A method asdefined in claim 3, wherein the direct cooling is effected by contactingthe coke with a heat-exchange fluid.
 5. A method as defined in claim 3,wherein the direct cooling is effected by contacting the coke withcoking water as a heat-exchange fluid.
 6. A method as defined in claim1; further comprising the step of sensing the temperature of thecoke/coal mixture; and effecting the adjustment of the coke temperatureas a function of the sensed temperature of the mixture.
 7. A briquettemade according to the method of claim 1.